(1) Field of the Invention
This invention relates to hydrocarbon polymer modifiers and their use in elastomeric compositions. More particularly, this invention relates to the use of hydrocarbon polymer modifiers in cured elastomeric compositions.
(2) Description of Related Art Including Information Disclosed under 37 CFR 1.97 and 1.98
Elastomeric compositions are used in a wide variety of applications, including tire components such as treads and sidewalls, hoses, belts, footwear components, and vibration isolation devices. The selection of ingredients for the commercial formulation of an elastomeric composition depends upon the balance of properties desired, the application, and the end use for the particular application.
For example, in the tire industry the balance between processing properties of the green (uncured) composition in the tire plant and in-service performance of the cured rubber tire composite is of particular importance. Conventional oil processing aids have been used in many tire components: tread compounds often contain polybutadiene rubber (“BR”), oil-extended polybutadiene rubber (“OE-BR”), styrene-butadiene rubber (“SBR”), oil-extended styrene-butadiene rubber (“OE-SBR”), isoprene-butadiene rubber (“IBR”), and styrene-isoprene-butadiene rubber (“SIBR”); sidewall and ply coats can contain butyl rubber and SBR and have used free aromatic oils as processing aids; internal components, such as the steel belt skim coat, gum strips, cushions, barriers, bases, and wedges, contain predominantly natural rubber and have used aromatic oils.
Generally, the raw ingredients and materials used in tire compounding impact all tire performance variables, thus, any new alternative to conventional processing oils must be compatible with the rubbers, not interfere with cure, be easily dispersed in all tire compounds, be cost effective, and not adversely impact tire performance. Rolling resistance, dry and wet skid characteristics, heat buildup, and so on are important performance characteristics, as well as the ability to improve the endurance of tires used in a wide variety of conditions, such as is required for agricultural tires, aircraft tires, earthmover tires, heavy-duty truck tires, mining tires, motorcycle tires, medium truck tires, and passenger car tires. On the other hand, maintaining ease of processability of the uncured elastomeric composition is also of significant importance. Additionally, the goals of improving air impermeability properties, flex fatigue properties, and the adhesion of the elastomeric composition to adjoining tire components without affecting the processability of the uncured elastomeric composition or while maintaining or improving the physical property performance of the cured elastomeric composition still remain.
Conventionally, various processing oils, such as naphthenic, paraffinic, and aromatic oils, have been added to most tire components to aid compound processing. Aromatic oil has been preferred due to its processing effectiveness and beneficial secondary properties, e.g., adhesion. However, these processing oils, particularly aromatic oils containing distilled aromatic extracts, are being replaced due to health, safety, and environmental concerns. For example, European Union Directive 2005/69/EC required the reduction of polycyclic aromatic hydrocarbons (“PAH”) in passenger car tires, light and heavy truck tires, agricultural tires, and motorcycle tires as of Jan. 1, 2010. Thus, rubber compounders have been replacing prior aromatic oils used in oil-extended (“OE”) rubbers with alternative oils or processing aids.
It is also known to improve tire tread performance by compounding amorphous or semicrystalline resins in the rubber base to improve tire performance, e.g., aliphatic resins having a high glass transition temperature (Tg). These materials can be miscible, which increases compound Tg for better wet traction, have some degree of immiscibility, which broadens compound Tg in wet traction region, or be immiscible in one or all of the polymers used, which has relatively no effect on the compound Tg. The immiscibility can be demonstrated by independent Tg peaks for the two different phases, i.e., the Tg corresponding to the rubber phase is not significantly changed by the immiscible resin. Tread compositions based on these formulations can have a low rolling resistance at normal use temperatures and/or a high grip at high temperature or “borderline” conditions.
In all cases, increasing the permanence of the oil, resin or other rubber compounding additive is important. Unfortunately, low molecular weight additives in general and immiscible resins in particular can migrate to the surface of the tread or other tire components over time, which can dramatically change the rubber compound characteristics and/or tire performance over its life. There is thus a need for improving the permanence of rubber compounding additives.